Emissions mandates relating to greenhouse gases as well as the opportunity for cost savings are motivating operators of processing plants (for example sewage digesters or garbage landfills) to install electrical power generating or cogeneration equipment that use methane-rich waste fuel produced by their plant processes.
Typically, the heat and electrical power produced by this equipment is used within the plant in support of the process. However, the composition and quantity of the fuel produced is not reliably stable over time. Hence, on occasions when the net energy available from the waste fuel is insufficient to fully support plant operation, these operators must choose between purchasing the needed additional electrical power, or switching their generator or cogeneration operation over to pipeline fuel.
Engine control systems exist today that are capable of adapting between two different fuels, i.e. running exclusively on either one fuel or the other (see for example EP0727574B1). Unfortunately, this prevents the system from utilizing the pipeline fuel to directly supplement the waste fuel by blending the pipeline fuel with the waste fuel.
Further, U.S. Pat. No. 6,805,107 teaches supplying a varying quality fuel as well as a constant quality fuel to an engine. However, the constant quality fuel is supplied from two separate outlets such that a constant flow is provided from one of the outlets as a base flow rate and an adjustable flow is provided from the second outlet. By providing the constant flow of constant quality fuel, the system of the '107 patent cannot allow a user to run the system entirely on varying quality fuel in the event that such fuel is of sufficient quality to power the system.
Another solution that has been attempted is using blending equipment external to the engine control system that endeavors to provide a constant fuel quality by blending pipeline fuel with the waste fuel. Reports on this type of system are that the performance and reliability have been very disappointing, in view of the high purchase cost.
The present invention relates to improved methods and apparatus over the state of the art.